The use of ECM systems, for example by the military, to block the reception of radio transmissions transmitted by other parties is well known. By blocking the reception of radio transmissions in this manner, voice communications can be disrupted, interfering with the transmission of information or instructions, and the remote control of devices such as improvised explosive devices or other remotely detonated explosives can be disrupted. Clearly, the disruption of the detonation of improvised, or other, explosive devices is beneficial in that the risk of injury to military personnel or civilians or damage to property and equipment is reduced, and disrupting the reception of voice communications can hamper organisation of personnel.
Whilst the use of ECM systems is beneficial in that it can disrupt voice communications or the reception of control signals transmitted by other parties, it has the disadvantage that communications by those operating the ECM system are also disrupted. It is desirable to provide a communications system whereby radio communications, either for voice or data transmission, can continue to be received by a party using an ECM system whilst that system is operative and without introducing vulnerabilities such as frequency gaps into the ECM transmission.